The present invention relates to an ignition unit for internal combustion engines with an ignition coil having a ferromagnetic core integrated into a spark plug connector, about whose main core is arranged a primary and secondary winding surrounded by an insulating body.
Such an ignition unit is already known from the DE-OS 37 20 826. In this prior art ignition unit, the ignition coil integrated with the spark plug connector essentially consists of a rod-shaped ferromagnetic core, of an inner cover cylinder made of an insulating material and surrounding the core, on the outer circumference of which is mounted the secondary winding, and of an external cover cylinder also consisting of insulating material and surrounding the secondary winding with a radial spacing, which carries the primary winding along its outer circumference. The interstices between the rod-shaped core, the inner cover cylinder and the outer cover cylinder are thereby filled with an electrically insulating filler or sealing compound. This ignition coil is so mounted on the associated spark plug connector that the axial directions of the elongated rod-shaped core and of the spark plug connector coincide. For integrating the spark plug connector with the rod-shaped ignition coil, the entire ignition unit is embedded in a casing or cover body made of an elastic insulating material.
The disadvantage of this already known ignition unit consists in particular in that it requires a very large installation space in the axial direction of the spark plug connector which can be traced back to the alignment of the ignition coil longitudinal axis in the axial direction of the spark plug connector. By reason of its large space requirement in the axial direction of the spark plug connector the known ignition unit is only inadequately suited for the installation in modern motor vehicle internal combustion engines because as low a structural height as possible is aimed at in these modern motor vehicle internal combustion engines by reason of the ever-decreasing space availability in the engine space of modern automobiles.
It is therefore the object of the present invention to provide an ignition unit of the aforementioned type consisting of a spark plug connector and of an ignition coil which, combined with best functioning, insulation safety, temperature resistance and vibration strength, is characterized by a small space requirement in the axial direction of the spark plug connector.
The underlying problems are solved according to the present invention in that the ignition coil and the spark plug connector are so arranged to one another that the axial directions of the spark plug connector and of the main core of the ignition coil form at least approximately a right angle.
It is achieved by this constructive arrangement of the ignition coil on the associated spark plug connector that the ignition unit has a minimum structural height in the axial direction of the spark plug connector. Owing to the arrangement of the ignition coil transversely to the axial direction of the spark plug connector, it becomes possible to accommodate the ignition unit consisting of the spark plug connector and of the ignition coil in the space which is available in customary cylinder heads of internal combustion engines for automobiles between the spark plug and the engine hood of the automobile and which up to now only served for the accommodation of the spark plug connector. An individual ignition coil-ignition system can be realized in this manner in which an ignition coil is directly coordinated to each individual spark plug. Such an individual ignition coil-ignition system offers the advantage that no open spark gaps exist and therebeyond, no high voltage ignition lines are required which, on the one hand, act as antennae and, on the other, can be easily damaged by animals, for example, Martens. An extraordinarily interference-free and functionally reliable ignition system can therefore be realized by the use of ignition systems according to the present invention.
According to a further feature of the present invention, the end areas of the main core carrying the primary and secondary winding are connected with each other by way of at least one core part disposed outside of the primary and secondary winding. Owing to this magnetic connection of the end areas of the main core, the magnetic stray or leakage field is minimized which leads to a considerable improvement of the efficiency.
Such a closed coil core is advantageously composed of two E-shaped halves whose center E-legs form together the main core. With this construction of the coil core the two center E-legs of the two E-shaped coil core halves can be introduced in a simple manner into the opening of the primary coil.
In order to achieve a uniform spark plug erosion, it is necessary that all ignition coils used in an individual coil ignition system have, to the greatest possible extent, the same inductance. The latter is determined decisively by a defined air gap in the coil core. With the use of a coil core of two E-shaped halves, this gap is provided preferably between the two center E-legs forming the main core. Owing to the arrangement of the air gap in the interior of the primary coil an undesired magnetic stray or leakage field can be avoided.
In order that the two E-shaped halves of the coil core cannot fall apart and in order that no stray or leakage field significantly impairing the efficiency of the ignition coil additionally occurs at the places, where the two E-shaped halves abut at one another, the outer legs of the two E-shaped halves are rigidly connected with each other.
It has thereby proven as particularly advantageous if the outer legs of the two E-shaped halves are welded together. An undesired air gap between the two coil core halves can be completely avoided by welding together the outer legs of the E-shaped halves of the coil core. A magnetic stray or leakage field which customarily occurs at such connecting places can thereby be nearly completely avoided in this manner, as a result of which an optimum efficiency of the ignition coil is assured. The air gap-free connection of the two coil core halves additionally offers the advantage that the ignition coil can be manufactured with only a small manufacturing tolerance as regards its inductance. The welding-together of the two coil core halves also offers the advantage compared to a threaded or riveted connection that no displacement of the magnetic flux takes place at the connecting places.
For purposes of a simple fastening of the entire ignition unit consisting of the spark plug connector and of the ignition coil at the cylinder head of an internal combustion engine, one bore each for receiving a fastening bolt is provided in the attachment areas of the outer legs of the two E-shaped halves of the coil core.
In order to maintain the cross section of the coil core within the area of the bores provided for the accommodation of fastening bolts, the attachment areas of the outer legs of the two E-shaped halves of the coil core are constructed reinforced, whereby the bores are arranged at least partly in the reinforced areas.
According to a preferred further feature of the present invention, the winding wires of the primary winding and/or of the secondary winding are wound in layers, whereby one insulating paper layer each is provided between the individual winding layers. As with this winding technique, the individual winding layers are additionally insulated with respect to one another by an insulating paper layer, in addition to the wire insulation, a very good insulation safety and dielectric strength is achieved.
The insulation safety of the ignition coil can be additionally optimized in that the winding wire sections of a winding layer are each arranged with a spacing to one another and the free spaces between the winding wire sections are filled out with a cast insulating material or filler compound.
Preferably the spacing of the winding wire sections amounts to about 5 to 10% of the respective winding wire diameter. This spacing of the winding wire sections represents an optimum as regards the two concurring goals; namely, to make the ignition coil as compact as possible, on the one hand, and to construct the same as safe with respect to insulation as possible, on the other.
According to a further feature of the present invention, the insulating body surrounding the primary and secondary winding consists completely of a cast material whereby it is cast in one piece without the use of a separate casing. On the one hand, such an insulating body can be manufactured cost-favorably (as no separate casing is required to be filled with the cast material) and, on the other, offers technical advantages compared to the known insulating body. Thus, in the insulating body according to the present invention, in contrast to the known insulating body, no differing thermal expansions can occur because it is made homogeneously of the same material. It therefore also does not possess any separating layer which with the known insulating body between the casing and the adjoining cast mass can lead to glow discharges.
In order to prevent a spark erosion between the coil core and the insulating body, the outer shape of the insulating body is so constructed that with the use of a coil core composed of two E-shaped halves the insulating body abuts far-reachingly at the inner circumference thereof.
By constructing the insulating body in the shape of a handle it is achieved that the entire ignition unit consisting of spark plug connector and ignition coil with coil core can be manually handled and gripped safely, especially in the installation at, respectively, disassembly from the cylinder head of an internal combustion engine.
According to a preferred further feature of the present invention, the primary connecting contacts connected with the primary coil are led out of the insulating body in the axial direction of the primary coil. This arrangement of the primary connecting contacts, by contrast to the arrangement of the primary connecting contacts of the primary coil in the axial direction of the spark plug connector, does not lead to an undesired increase of the structural height of the ignition unit in the axial direction of the spark plug connector.
Advantageously, the primary connecting contacts are thereby arranged in a plug-like extension of the insulating body. Preferably detents for lockingly engaging a corresponding plug extending over the plug-like extension are provided at the extension of the insulating body. A safe plug connection is achieved by the detent connection of the corresponding plug extending over the plug-shaped extension.
According to a preferred further development of the present invention, a contact element electrically connected with the secondary winding is provided at the end of the insulating body facing the spark plug connector, by means of which a safe contact with the spark plug connector is established.
For compensating a possible axial displacement between the axis of the spark plug and therewith also of the emplaced spark plug connector and of the axis of the ignition coil threadably fastened at the cylinder head of the combustion engine, a joint-like movable, electrically conducting connection is provided between the contact element and the electrically conducting part of the spark plug connector. Preferably, this joint-like movable, electrically conducting connection is formed by a spring element which can be manufactured in a cost-favorable manner.
In order to be able to additionally compensate for the tolerances and vibrational movements between the spark plug and the ignition unit consisting of the spark plug connector and of the ignition coil fastened at the cylinder head of the combustion engine, which occur in the axial direction of the spark plug, a coil spring conically enlarged up to its free end is provided as contact part of the spark plug connector acting on the center electrode of the respective spark plug. Owing to the conical construction of the coil spring, in addition to a good contact by reason of the large abutment area at the also conical spark plug center electrode, also a simple mounting of the ignition unit on the spark plug is assured.
In order to prevent a penetration of moisture into the contact area between the spark plug center electrode and the contact part of the spark plug connector, according to a still further feature of the present invention, a casing is provided as part of the spark plug connector which protrudes beyond the contact part of the spark plug connector and forms a socket that completely covers the (porcelain) spark plug neck and circumferentially abuts securely at the threaded head of the spark plug.
In order to attain, on the one hand, a good press fit of the socket end on the threaded head of the spark plug and, on the other, an easy threading of the spark plug neck into the socket, the inner diameter of the socket increases towards the outside within the area of its free end. As the socket end must circumferentially securely abut with a press fit at the threaded head of the spark plug, it is necessary that the casing of the spark plug connector be flexible. It is therefore made advantageously of an elastic silicon rubber.